The present invention relates to a method of fabricating a semiconductor laser device and a semiconductor laser device. In particular, the present invention relates to a method of fabricating a semiconductor laser device, which is capable of peeling a device formation region from a substrate and simultaneously forming a resonance mirror of the semiconductor laser device, and a semiconductor laser device fabricated by the fabrication method.
Methods of fabricating a semiconductor laser device have been known. One of the methods involves forming nitride semiconductor layers on a sapphire substrate by crystal growth and dividing the semiconductor layers into individual semiconductor laser devices. With respect to such a fabrication method, since a resonance mirror exerts a large effect on characteristics of a semiconductor laser device, the method of forming the resonance mirror has been regarded as one of important techniques; particularly, in the fabrication of a GaN based semiconductor laser. One of the methods of forming a resonance mirror includes the step of isolating devices from each other by cleavage or etching, wherein an end plane of each of the devices simultaneously formed is taken as a resonance mirror.
In the case of isolating devices from each other by cleavage, device isolation grooves for isolating the devices from each other are formed by etching, and then devices are isolated from each other by cleavage along the device isolation grooves.
In the case of isolating devices from each other by etching, the depth of grooves for isolating the devices from each other must reach the lowermost layer of semiconductor layers from which the devices are to be formed.
In some cases, cleavage is performed without being accompanied by peeling devices from a substrate. In this case, when the devices are isolated from each other by cleavage, the substrate is simultaneously cleaved.
The method of isolating devices from each other by making use of cleavage or etching is disadvantageous in that the crystal of a device isolation plane of each of the devices may be damaged at the time of isolating the devices from each other.
With respect to the quality of a resonance mirror of a device, a semiconductor laser device particularly requires a flat resonance mirror with less damage of crystal. Accordingly, it has been expected to develop a fabrication method capable of forming a high quality resonance mirror without increasing the number of fabrication steps.
In the process of fabricating a GaN based semiconductor device, devices in the form of chips are often isolated from each other by using a dicer or the like. Such a process requires much labor to isolate the devices from each other, and has much difficulty in finely isolating the devices from each other while avoiding electrodes and the like spread in the horizontal direction. This process has another disadvantage that, since sapphire substrate and a nitride such as GaN each have a high hardness, a cutting margin of at least 20 xcexcm is required for dicing, thereby making it further difficult to finely isolate chips from each other by dicing.
In the case of dividing nitride semiconductor layers stacked on a sapphire substrate into individual semiconductor laser devices by cleavage, since not only the nitride semiconductor layers constituting main portions of the devices but also the sapphire substrate is cleaved, the sapphire substrate cannot be repeatedly used for fabricating semiconductor laser devices.
In the case of isolating devices from each other by making use of dry etching or dicing, in general, the crystal of a device isolation plane of each of the devices is necessarily damaged. As such, even if through-dislocations from the substrate side and the like are suppressed during fabrication of semiconductor laser devices, crystal characteristics of the devices are degraded by dry etching or dicing at the final isolation step. The use of dry etching or dicing for isolating devices from each other is also disadvantageous in correspondingly increasing the number of fabrication steps.
For a semiconductor laser device using GaN semiconductors, in the case of forming an end plane of the semiconductor laser by cleavage or etching, since each of the GaN semiconductors have a hexagonal crystal structure, it is difficult to form a flat end plane as compared with another type of semiconductor laser. If an end face of a device is tilted or uneven, a reflectance is degraded, thereby increasing a threshold value of a current required for laser oscillation.
An object of the present invention is to provide a method of fabricating a semiconductor laser device, which is capable of peeling devices from a substrate and isolating the devices from each other, and simultaneously forming a flat resonance mirror with less damage of crystal on an end plane of each of the devices in one fabrication step, and to provide a semiconductor laser device fabricated by the fabrication method.
To achieve the above object, according to a first embodiment of the present invention, there is provided a method of fabricating a semiconductor laser device, including the steps of: forming semiconductor layers composed of a first conductive type cladding layer, an active layer, and a second conductive type cladding layer on a substrate; and peeling a device formation region of the semiconductor layers from the substrate and simultaneously forming a resonance mirror on an end portion of the device formation region by irradiating the device formation region with energy beams traveling from the back surface side of the substrate.
With this configuration, since the semiconductor layers composed of the first conductive type cladding layer, the active layer, and the second conductive type cladding layer are formed on the substrate and each of semiconductor laser devices mainly formed by the semiconductor layers is irradiated with energy beams, it is possible to carry out the step of peeling the devices from the substrate simultaneously with the step of isolating the devices from each other. At this time, since the semiconductor layers can be cleaved by irradiating the semiconductor layers with energy beams traveling from the back surface side of the substrate, the devices can be isolated from each other easily. Also, by selectively irradiating a region defined by projecting a bottom plane of the semiconductor laser device to the back surface of the substrate, the semiconductor laser having a specific size can be fabricated. Further, since the end plane of a semiconductor laser device formed by isolation of the device from another device is flattened and has less damage of crystal, the performance of the semiconductor laser device can be enhanced by using the end plane of the device as a resonance mirror. In addition, by forming a window region while avoiding the vicinity of a portion corresponding to the resonance mirror to be formed by isolation of a semiconductor laser device, it is possible to more easily isolate the device from another device.
According to a second embodiment of the present invention, there is provided a method of fabricating a semiconductor laser device, including the steps of: forming a selective growth mask having an opening portion formed into a stripe shape on a base body; forming a crystal layer by selective growth from the opening portion; forming semiconductor layers composed of a first conductive type cladding layer, an active layer, and a second conductive type cladding layer on the crystal layer; and peeling a device formation region of the crystal layer and the semiconductor layers from the base body and simultaneously forming a resonance mirror on an end portion of the device formation region by irradiating the device formation region with energy beams traveling from the back surface side of the base body. In particular, since the semiconductor layer having a tilt crystal plane tilted from the principal plane of the substrate has desirable crystallinity and allows formation of a flat resonance mirror perpendicular to the semiconductor layers, it is possible to form a high performance semiconductor laser device by using such a semiconductor layer having a tilt crystal plane.
According to the method of fabricating a semiconductor laser device of the present invention, since the step of peeling the devices from the substrate can be carried out simultaneously with the step of isolating the devices from each other, it is possible to simplify the fabrication process and, hence, to reduce the fabrication cost.
In addition, the method of fabricating a semiconductor laser device according to the present invention can be applied to a method of fabricating a device other than a semiconductor laser device. Even in this case, since the step of peeling devices from a substrate can be carried out simultaneously with the step of isolating the devices from each other, the fabrication process can be simplified.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.